To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SOMA) as an advanced access technology have been developed.
Before a UE and a mobile network access point can communicate, the UE must first connect to the network. A random-access channel (RACH) is a shared channel used by UEs to access the mobile network, without requiring prior knowledge of the network. For the example of an LTE UE, there can be many frequencies available through which the UE could connect to multiple network operators. The UE must synchronize to each frequency in turn to establish it corresponds to an appropriate operator. This is achieved through an initial synchronisation process. Once synchronized to a particular frequency, the UE can determine whether it corresponds to an appropriate operator through the master information and System information blocks transmitted periodically by each network. The next step is known as the Random Access Procedure which allows the network to identify that a UE is trying to connect. The first message of the random access procedure comprises the UE sending a specific RACH preamble over the shared RACH. The identity of the UE is also transmitted. If the RACH preamble is received by the LTE base station (the evolved Node B, eNB) it sends a random access response including an uplink grant resource for further communication between the UE and the eNB, specifically for the transmission of a Radio Resource Control (RRC) Connection Request message by the UE in which the UE seeks permission to connect to the network.
In a conventional cellular scenario, such as LTE, the antenna pattern of the base station is sectorized and the antenna pattern of the UE is most likely omnidirectional. Therefore, the reception of the random access preamble sent by the UE (within an RA Channel, RACH) is principally affected by the distance between the eNB and the UE. In a mm-wave network, due to the hostile propagation conditions (severe path loss and vulnerability to blockage), beam-foil ling transmission is employed at both the mmSC and the UE to tackle the increased path loss. However, the high directivity in mm-wave technologies makes the conventional design of initial access procedures (such as for LTE based on broadcast signals) unsuitable. Therefore, for a mm-wave initial access procedure there is a need to pair the beams of a mmSC and a UE, which may take a considerable amount of time.